[TowerTalk] Ferrite beads for common mode current

[Ian White GM3SEK]

jeremy-ca wrote:
>By going from the conventional to the crossover method I was able to 
>get a G5RV to cooperate that I was using at the summer cottage decades 
>ago. No amount of twidling of the conventional turns worked.
>At that time and a few hundred miles from the test equipment at work I 
>was more interested in getting on the air than the whys. Obviously I 
>had found a "sweet" spot.
>
That can easily  happen, as the equivalent lumped capacitance is only a 
few pF so the resonant frequency is extremely sensitive to small 
variations in strays. Even a twisted-wire 'gimmick' capacitor connected 
end-to-end to the outside of the shield can move the resonance by a few 
MHz at 20MHz.

If I desperately wanted to trim the resonance to some exact frequency, 
the best way would probably be a gimmick cap with a GDO. However, the 
peak is usually large enough and broad enough to make that degree of 
refinement unnecessary.


-- 

73 from Ian GM3SEK